The present invention relates to a cooling structure for integrated circuits (IC's), and more particularly to a cooling structure which cools IC's by circulating a liquid coolant, such as water, in the vicinity of the IC's and causing heat generated by the IC's to be conducted to the liquid coolant.
Examples of this kind of prior art cooling structure are disclosed in an article entitled "A Conduction-Cooled Module for High-Performance LSI Devices" by S. Oktay and H. C. Kammerer, published in IBM J. RES. DEVELOP, Vol. 26, No. 1, Jan. 1982 and Japanese Patent Application Disclosure No. Sho 60-160150.
The former article discloses a structure which causes heat generated by an IC on a wiring board to be conducted to a cold plate via a piston, a gap filled with helium gas, a hat and an interposer by pressing the piston, whose contact face is spherical, against a heat-radiating face of the IC with the pressure of a spring, and cooling the cold plate with a cooling medium.
The latter article teaches a structure which comprises a heat transfer substrate, a variable-shape heat conductor and a heat transfer plate arranged over heat radiating faces of chips on a printed wiring board together with a variable-elasticity bellows, and achieves cooling by spraying a liquid coolant from a nozzle over the heat transfer plate within the bellows.
These prior art cooling structures, however, have the following disadvantages:
First, regarding the cooling structure referred to first, the mechanism to constantly keep the piston pressed against the heat radiating face of the IC with the elastic force of the spring invites a load on the connecting part between the IC and the wiring board and thereby deteriorates the reliability of the connecting part.
Second, this cooling structure, in which the face of the piston coming into contact with the IC is spherically shaped and a gap is provided between the hat and the piston to absorb fluctuations in height and inclination which occur when the IC is fitted to the wiring board. However, the cooling efficiency is reduced by the limitation this configuration imposes on the effective heat transfer area.
Third, in the same cooling structure, the path of the coolant flow in the cold plate for heat transfer is formed by forced convection, resulting in a heat transfer coefficient of no more than 0.1 to 0.5 W/cm.sup.2 .degree. C., and accordingly the cooling capacity will prove to be insufficient if the power consumption rises with an increase in the degree of circuit integration.
Fourth, the cooling structure cited second, because of its configuration of the heat transfer substrate, with the variable-shape heat conductor and heat transfer plate intervening between the liquid coolant sprayed from the nozzle and the chips which are the sources of heat, is unable to attain a high enough heat conductivity, resulting in an insufficient cooling capacity.